1. Field of the Invention
Particularly, the present invention relates to a magnetic sensing element in which PW50 (half-amplitude pulse width) and SN ratio (Signal to Noise Ratio) are improved more than before without causing a decrease in reproducing characteristics such as rate of change in resistance (Δ R/R) and which is thus suitable for increasing recording density, and a method for manufacturing the same.
2. Description of the Related Art
Typically, tunneling magnetoresistive elements have such a structure that a multilayered film, which makes use of a tunneling magnetoresistance effect, is interposed between lower and upper shied layers that are opposed to each other in a film thickness direction.
More specifically, the multilayered film is formed by depositing, for example, an underlying layer, an antiferromagnetic layer, a pinned magnetic layer, an insulating barrier layer, a free magnetic layer, and a protective layer on the lower shied layer in the that order from the bottom.
In the prior art, generally, the underlying layer has been composed of Ta, which is a nonmagnetic material. For example, Patent Document 1 discloses in the paragraph [0056] a case where Ta is used as an underlying layer.
Patent Document 1:
Japanese Unexamined Patent Application Publication No 2001-176027
Patent Document 2:
Japanese Unexamined Patent Application Publication No 2001-52316
Patent Document 3:
Japanese Unexamined Patent Application Publication No 2001-28108
In order to increase recording density, it is necessary to be able to accurately read data recorded at small bit intervals, and for this purpose, it is important to decrease a half-amplitude pulse width (PW50).
In order to decrease the half-amplitude pulse width (PW50), it is effective to decrease a gap length (GL) obtained from a distance between upper and lower shield layers. In tunneling magnetic sensing elements having a conventional configuration, the gap length between the upper and lower shields corresponds to a film thickness of a multilayered film interposed between the upper and lower shields.
Thus, the gap length can be decreased by simply reducing the film thickness of the multilayered film, but individual layers of the multilayered film already have a film thickness as thin as a few tens of A. Therefore, it is desirable to realize a narrow gap with a minimum change in film thickness of the individual layers.
When narrowing the gap, moreover, it has to be avoided to cause deterioration of reproducing characteristics such as rate of change in resistance (Δ R/R).
In short, it has been desired to decrease the half-amplitude pulse width (PW50) by narrowing the gap while avoiding a decrease in the rate of change in resistance (Δ R/R). In the prior art, however, no improvement has been made, particularly, on the underlying layer, which is to be disposed in contact with the lower shield layer, so as to facilitate narrowing the gap without deteriorating reproducing characteristics.